I'm unable to cancel my pending purchases from the App Store

I downloaded an app that offered a free trial but I went through the purchasing too quickly to realize it was going to charge me a year subscription instead of a free trial, I don’t have $135 to complete the purchase and I have no way of cancelling it, I’m just looking for a way to cancel this purchase since it was intended to be a free trial anyways so that I can resume using the App Store as my account is basically blocked right now until it’s able to charge my card for something that wasn’t even supposed to be charged. Any help is appreciated!

[Re-Titled by Moderator]